Battery systems may be used to provide power in a wide variety of applications. Exemplary transportation applications include hybrid electric vehicles (HEV), electric vehicles (EV), heavy duty vehicles (HDV) and vehicles with 42-volt electrical systems. Exemplary stationary applications include backup power for telecommunications systems, uninterruptible power supplies (UPS), and distributed power generation applications.
Examples of the types of batteries that are used include nickel metal hydride (NiMH) batteries, lead-acid batteries, and other types of batteries. A battery system may include a plurality of battery subpacks that are connected in series and/or in parallel. The battery subpacks may include a plurality of batteries that are connected in parallel and/or in series.
Inherent properties of a battery can dictate a minimum operating voltage specification (Vmin) and/or a maximum operating voltage specification (Vmax). In some applications Vmin and Vmax can be specified by engineers and based on other criteria. When taken together Vmin and Vmax indicate a voltage range that the battery voltage should be kept within to maximize the service life of the battery. Vmin and Vmax also infer limits on the battery's abilities to provide power during discharge and accept power during recharge. In some applications, such as HEVs, these limits on battery power can periodically limit the performance of the vehicle. For example, an HEV control system can limit the acceleration of the vehicle to keep the battery voltage above the minimum battery voltage Vmin. The HEV control system can also limit a regenerative braking function of the vehicle to keep the battery voltage below the maximum battery voltage Vmax and thereby maintain some regenerative braking capacity.
One method of preventing the acceleration performance limit from occurring is to use an internal combustion engine to supplement the power delivered from the battery. Such a method introduces other issues, however. For example, the engine may be turned off when it is needed. In such a situation the vehicle performance will still be limited for a brief period while the HEV control system starts the engine.
A second method of preventing the performance limits is to leave the engine idling so that it is always available to supplement the battery power. However an idling engine wastes fuel and therefore does not provide an ideal solution. As such, there remains a need for predicting battery power limits and synchronizing supplemental power sources with load demands.